A so-called hybrid vehicle that is driven by an internal combustion engine and an electric motor receives attention. When the hybrid vehicle decelerates, the electric motor functions as an electric generator in order to perform an electric power regeneration (hereinafter, also simply referred to as a regeneration) and store the electric power. The stored electric power is used for generating driving force, for example, when the vehicle accelerates or runs.
Some hybrid vehicles have a gear box configured to automatically shift gears. Hereinafter, the gear box is also referred to as a transmission.
In such cases, a clutch that connects the power or cuts the connection of the power can be provided between the internal combustion engine and the electric motor.
Some conventional vehicles include an internal combustion engine, an electric machine capable of operating as an electric motor and as an electric generator, a clutch, a gear box of which transfer ratio is variable, a power electronics, and an electric energy storage device. The clutch is provided between the internal combustion engine and the gear box. The driving torque can be led through the clutch from the internal combustion engine to the gear box and from the electric machine to the internal combustion engine. The electric machine is provided between the only clutch placed between the internal combustion engine and the gear box, and the gear box so that the electric machine can directly transfer positive torque or negative torque to the gear box input shaft of the gear box (for example, see patent literature PTL1).